This is a principle borne of experience. There have been a number of cases where a new fatal-error check killed a bunch of systems that apparently were working

This is a principle borne of experience. There have been a number of cases where a new fatal-error check killed a bunch of systems that apparently were working for a long time before. Usually it is preferred to WARN_ONCE() but not BUG_ON(). Otherwise, big corporate users, or a wide random assortment of desktop users, end up going back to an older kernel to make their systems work. The linux kernel tries above all to never have regressions, even if these regressions are just catching probably very bad bugs that were just not caught before. This happens, often enough! Think of this from the lense of natural selection. There are many many subtle tricky low-level bugs that can result in memory corruption - many drivers, many features, many optimizations, many "cleanups", a surprisingly high rate of code changes. Many of them are caught when they cause problematic corruption. Others, just due to luck, very rarely cause any visible problem, - for months or years. We do want to know about them. We do not want to suicide the whole system, it may be one of those rare bugs that made it this far because it's usually (surprisingly) not fatal on its own.